Pergamon Appl. Radiat. Isot. Vol. 48, No. 2, pp. 225 235, 1997 Copyright ,i: 1997 Elsevier Science Ltd Printed in Great Britain. All rights reserved PII: S0969-8043(96)00183-2 o969-8o43/97 $17.oo + o.oo On-line Flow Visualization in Multiphase Reactors using Neural Networks L. GODFROY ~, F. LARACHI 2, G. KENNEDY ~, B. GRANDJEAN 3 and J. CHAOUKI *1 'Department of Chemical Engineering, l~cole Polytechnique, C.P. 6079, Station 'Centre-Ville', Montr6al, Quebec, Canada H3C 3A7, -'Department of Chemical Engineering, Laval University, Sainte-Foy, Quebec, Canada GIK 7P4 and 'Nuclear Engineering Institute, Ecole Polytechnique. C.P. 6079, Station "Centre-Ville', Montr6al, Quebec, Canada H3C 3A7 (Receivedjbr publication 20 June 1996) The success of the radioactive particle tracking system (RPT) developed at the Ecole Polytechnique (Montr6al) and applied to the study of particle motion in a variety of chemical reactors (three-phase fluidized bed, gas spouted bed and liquid fluidized bed) has motivated us to continue improving this technique (in terms of accuracy and resolution) and to apply it to new reactor types. Our goals are: (i} to enhance the original search location algorithm in order to permit on-line flow visualization and 0il to extend RPT to very fast solids flows, such as those encountered in circulating fluidized beds (particle velocities higher than a few m s ~). The potential of neural networks for on-line and real-time visualization of particle movements in multiphase reactors will be illustraled. The original least-squares search location algorithm (Larachi et al., 1994) has been replaced with an enhanced algorithm which uses a three-layer feedforward neural network. The results obtained from the two algorithms for particle tracking in a three-phase fluidized bed reactor are compared. The RPT system employs 8 NaI(TII scintillation detectors to study the movement of solid particles in chemical reactors. The performance of the system was investigated using particles containing the radioisotopes 4~Sc(,'-ray energy 1005 keV), "Mo (7-ray energy 140 keV) and ~SAu (3,-ray energy 412 keV). The three-dimensional spatial resolution was measured in empty and water-filled tubes, simulating highly diluted and dense media. The best results were obtained using '~SAu with which the particle can be located to within 7 mm in water and 9 mm in air 100 times s ~. Copyright 1997 Elsevier Science Ltd Background It is well recognized that the measurement of particle trajectories and related dynamic phenomena in fluid-particulate flow systems is particularly difficult, because the particles usually exhibit complex motion patterns and the flow field, very often, is spatially non-uniform. Conventional measuring devices, such as fiber optics or electrical capacitance probes, give large errors because they disturb the flow; they also do not provide full flow field measurements. Given accurate knowledge of the particle movement, one can infer a wealth of transient and steady-state information on the particulate phase, such as the circulation time distribution and the time-averaged velocity field. Notable examples of two and three-phase flow conditions, where accurate trajec- tory measurements of solid particles are critical, are found in fluid-solid transport processes such as drying, combustion and hydrorefining. In each of these areas, the accurate and non-invasive measure- ment of particle movement would advance the *To whom all correspondence should be addressed. physical understanding and the modeling of the related technologies. In the last decade, important progress has been made in the development of advanced non-invasive nuclear particle tracking techniques specifically suited for the characterization of three-dimensional flow fields of discrete or continuous batch phases in dilute dense and opaque multiphase systems (Chaouki et al., 1996). Two photon emission-based tracking techniques are currently in application on laboratory scale reactors: 'positron emission particle tracking (PEPT)" (Broadbent el al., 1993): and ';'-ray emission radioactive particle tracking (RPT)" (Lin et al., 1985: Moslemian et al., 1992 and Larachi et ell., 1994). Both use the detection and counting of highly penetrating ;'-rays emitted by radiolabeled flow followers which are dynamically similar to the tracked phase. They use the detected ;'-rays to provide the instantaneous coordinates (x( t ),y(t ),c( t )) of the moving tagged particle. The success of the radioactive particle tracking system developed at the E, cole Polytechnique (Larachi et al., 1994) and applied to the study of particle motion in three-phase fluidized beds, gas 225